A basic method for restoring the power envelope from a reverberant signal was proposed by Hirobayashi et al. This method is based on the concept of the modulation transfer function (MTF) and does not require that the impulse response of an environment be measured. However this basic method has the following problems: (i) how to precisely extract the power envelope from the observed signal; (ii) how to determine the parameters of the impulse response of the room acoustics; and (iii) a lack of consideration as to whether the MTF concept can be applied to a more realistic signal. This paper improves this basic method with regard to these problems in order to extend this method as a first step towards the development for speech applications. We have carried out 1,500 simulations for restoring the power envelope from reverberant signals in which the power envelopes are three types of sinusoidal, harmonics, and band-limited noise and the carriers are white noise, to evaluate our improved method with regard to (i) and (ii). We then have carried out the same simulations in which the carriers are two types of carrier of white noise or harmonics with regard to (iii). Our results have shown that the improved method can adequately restore the power envelope from a reverberant signal and will be able to be applied for speech envelope restoration.
Abstract:We previously proposed an improved method for restoring the power envelope from a reverberant signal, based on the modulation transfer function (MTF) concept in order to resolve the problems of Hirobayashi's method. In this paper, to apply our improved method to reverberant speech, we consider three issues related to speech applications: (i) how to apply the improved method to speech dereverberation based on co-modulation characteristics; (ii) whether the MTF concept can also be applied in the sub-band for reverberant signals; and (iii) whether power envelope inverse filtering should be done separately in each channel. We propose an extended filterbank model based on these considerations. We have carried out 15,000 simulations of the power envelope restoration for reverberant speech signals, and our results have shown that the proposed model can adequately restore the power envelopes in all channels from reverberant speech signals. We also found that the estimation of the reverberation time should be done separately in each channel to improve the restoration accuracy of the power envelope.
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